1. Field of the Invention
The present invention relates to three dimensional (3D) packaging, and more particularly, to the integration of through-silicon vias (TSVs).
2. Discussion of Related Art
3D packaging is emerging as a solution for microelectronics development toward system on chip (SOC) and system in package (SIP). In particular, 3D flip chip structures with TSVs have the potential for being widely adopted. TSV 3D packages generally contain two or more chips stacked vertically, with vias through silicon substrates replacing edge wiring to create an electrical connection between the circuit elements on each chip.
During TSV processing a device wafer is typically thinned back to 50-100 μm in thickness. Wafers this thin cannot be handled successfully without some type of support system to hold the wafers flat and to protect the fragile thinned wafer from mechanical damage such as chipping, cracking, etc.
Current TSV processes typically include attaching the device wafer to a temporary support wafer using a temporary adhesive and then detaching the thinned device wafer from the support wafer at the end of the process flow sequence. Several implementations may be used for detaching the thinned device wafer from the support wafer.
In a first implementation, a thermal release is used. In this implementation a thermoplastic adhesive is used to temporarily bond the device wafer to a temporary support wafer. Once the TSV processing is completed, heat is used to soften the adhesive and then the thinned device wafer is mechanically separated from the temporary support wafer.
In a second implementation, an ultraviolet (UV) release is used. In this implementation the device wafer is attached to a temporary glass carrier wafer using a UV-curable temporary adhesive in conjunction with a light-to-heat conversion (LTHC) release coating. After TSV processing is completed, laser radiation is applied through the glass carrier wafer to the LTHC layer, thus weakening it. The glass carrier is then lifted off of the thinned device wafer, and then the UV-curable adhesive is peeled off of the thinned device wafer.
In a third implementation, a solvent release is used. In this implementation the device wafer is attached to a perforated temporary carrier wafer using a temporary adhesive. Once TSV processing is completed, a solvent is applied through the perforations in the temporary carrier wafer to dissolve away the temporary adhesive.
In each of the three implementations the temporary adhesives are all mechanically soft, and offer minimal protection to the fragile device wafer against mechanical damage during TSV processing.